FIG. 1 illustrates a network structure of an E-UMTS (Evolved-Universal Mobile Telecommunications System). An E-UMTS is a system evolving from the conventional WCDMA (wideband code division multiple access) UMTS and its basic standardization is currently handled by the 3GPP (3rd Generation Partnership Project). The E-UMTS can also be called an LTE (Long Term Evolution) system.
Referring to FIG. 1, an E-UTRAN (UMTS terrestrial radio access network) includes base stations (hereinafter, referred to as ‘eNode B’ or ‘eNB’), wherein the respective eNBs are connected with each other through X2 interface. Also, each of eNBs is connected with a user equipment (UE) through a radio interface and connected with an EPC (Evolved Packet Core) through S1 interface. The EPC includes MME/SAE gateway (Mobility Management Entity/System Architecture Evolution gateway).
Layers of a radio interface protocol between a UE and a network can be classified into a first layer L1, a second layer L2 and a third layer L3 based on three lower layers of OSI (open system interconnection) standard model widely known in communication systems. A physical layer belonging to the first layer L1 provides an information transfer service using a physical channel. A radio resource control (hereinafter, abbreviated as ‘RRC’) layer located at the third layer plays a role in controlling radio resources between the UE and the network. For this, the RRC layer enables RRC messages to be exchanged between the UE and the network. The RRC layer may distributively be located at network nodes including Node B, an AG and the like, or may independently be located at either the Node B or the AG.
FIG. 2 is a schematic view illustrating an E-UTRAN (UMTS terrestrial radio access network). In FIG. 2, a hatching part represents functional entities of a user plane and a non-hatching part represents functional entities of a control plane.
FIG. 3A and FIG. 3B illustrate a structure of a radio interface protocol between the user equipment (UE) and the E-UTRAN, in which FIG. 3A is a schematic view of a control plane protocol and FIG. 3B is a schematic view of a user plane protocol. Referring to FIG. 3A and FIG. 3B, a radio interface protocol horizontally includes a physical layer, a data link layer, and a network layer and vertically includes a user plane for data information transfer and a control plane for signaling transfer. The protocol layers in FIG. 3A and FIG. 3B can be classified into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The physical layer as the first layer provides information transfer service to an upper layer using physical channels. The physical layer (PHY) is connected to a medium access control (hereinafter, abbreviated as ‘MAC’) layer above the physical layer via a transport channel. Data are transferred between the medium access control layer and the physical layer via the transport channel. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel. The physical channel of the E-UMTS is modulated according to an orthogonal frequency division multiplexing (OFDM) scheme, and time and frequency are used as radio resources.
The medium access control (hereinafter, abbreviated as ‘MAC’) layer of the second layer provides a service to a radio link control (hereinafter, abbreviated as ‘RLC’) layer above the MAC layer via a logical channel. The RLC layer of the second layer supports reliable data transfer. In order to effectively transmit IP packets (e.g., IPv4 or IPv6) within a radio-communication period having a relatively narrow bandwidth, a PDCP layer of the second layer (L2) performs header compression to reduce unnecessary control information.
A radio resource control (hereinafter, abbreviated as ‘RRC’) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers (hereinafter, abbreviated as ‘RBs’) to be in charge of controlling the logical, transport and physical channels. In this case, the RB means a service provided by the second layer for the data transfer between the UE and the UTRAN.
In the aforementioned protocol layer structure, a data processing method in a specific layer, for example, MAC layer will be described below. The MAC layer receives an upper layer data block (i.e., RLC PDU: RLC protocol data unit) from its upper layer, i.e., RLC layer through the logical channel to configure a lower layer data block (i.e., MAC PDU) according to MAC layer protocol. The lower layer data block includes at least one MAC SDU (Service Data Unit) and header, which include a part or all of the data upper layer blocks. The header means control information related to at least one MAC SDU included in the MAC PDU, and includes information (LCID: Logical Channel Identifier) indicating a logical channel to which a corresponding MAC SDU is transferred, and a length field indicating a length of the corresponding MAC SDU.
The length field included in the header can be comprised of 7 bits or 15 bits. For example, considering that one length field is allocated per MAC SDU having a size of 100 bits to 200 bits, voice packets occupy a considerable part in one MAC PDU, thereby causing channel resources to be wasted in the overall system. In particular, if data of a constant size are generated at a constant time interval, such as voice packets or MBMS (Multicast and Broadcasting Multimedia Service) packets, a length field of 7 bits or 15 bits is allocated per MAC SDU. In this case, a problem occurs in that overhead may be caused in the system.